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lapping wikipedia jump to content main menu main menu move to sidebar hide navigation main page contents current events random article about wikipedia contact us contribute help learn to edit community portal recent changes upload file special pages search search appearance donate create account log in personal tools donate create account log in contents move to sidebar hide top 1 operation 2 two piece lapping 3 accuracy and surface roughness 4 measurement toggle measurement subsection 4 1 flatness 4 2 roughness 5 see also 6 references 7 external links toggle the table of contents lapping 19 languages azərbaycanca български čeština deutsch español فارسی français hrvatski bahasa indonesia italiano nederlands norsk bokmål polski română русский slovenčina svenska தமிழ் українська edit links article talk english read edit view history tools tools move to sidebar hide actions read edit view history general what links here related changes upload file permanent link page information cite this page get shortened url switch to legacy parser print export download as pdf printable version in other projects wikidata item appearance move to sidebar hide from wikipedia the free encyclopedia process of removing material from two workpieces this article is about the machining operation for other uses see lapping disambiguation this article needs more citations please help improve this article by adding citations to reliable sources unsourced material may be challenged and removed find sources lapping news newspapers books scholar jstor august 2009 learn how and when to remove this message lapping machine lapping is a machining process in which two surfaces are rubbed together with an abrasive between them by hand movement or using a machine lapping often follows other subtractive processes with more aggressive material removal as a first step such as milling and or grinding lapping can take two forms the first type of lapping traditionally often called grinding involves rubbing a brittle material such as glass against a surface such as iron or glass itself also known as the lap or grinding tool with an abrasive such as aluminum oxide jeweller s rouge optician s rouge emery silicon carbide diamond etc between them this produces microscopic conchoidal fractures as the abrasive rolls about between the two surfaces and removes material from both the other form of lapping involves a softer material such as pitch or a ceramic for the lap which is charged with the abrasive the lap is then used to cut a harder material the workpiece the abrasive embeds within the softer material which holds it and permits it to score across and cut the harder material taken to a finer limit this will produce a polished surface such as with a polishing cloth on an automobile or a polishing cloth or polishing pitch upon glass or steel taken to the ultimate limit with the aid of accurate interferometry and specialized polishing machines or skilled hand polishing lensmakers can produce surfaces that are flat to better than 30 nanometers this is one twentieth of the wavelength of light from the commonly used 632 8 nm helium neon laser light source surfaces this flat can be molecularly bonded optically contacted by bringing them together under the right conditions this is not the same as the wringing effect of johansson blocks although it is similar operation edit small lapping plate made of cast iron a piece of lead may be used as the lap charged with emery and used to cut a piece of hardened steel the small plate shown in the first picture is a hand lapping plate that particular plate is made of cast iron in use a slurry of emery powder would be spread on the plate and the workpiece simply rubbed against the plate usually in a figure eight pattern small lapping machine the second picture is of a commercially available lapping machine the lap or lapping plate in this machine is 30 cm 12 in in diameter about the smallest size available commercially at the other end of the size spectrum machines with 2 4 to 3 0 metre diameter 8 to 10 ft plates are not uncommon and systems with tables 9 m 30 ft in diameter have been constructed referring to the second picture again the lap is the large circular disk on the top of the machine on top of the lap are two rings the workpiece would be placed inside one of these rings a weight would then be placed on top of the workpiece the weights can also be seen in the picture along with two fiber spacer disks that are used to even the load in operation the rings stay in one location as the lapping plate rotates beneath them in this machine a small slurry pump can be seen at the side this pump feeds abrasive slurry onto the rotating lapping plate logitech lapping machine and retention jig when there is a requirement to lap very small specimens from 75 mm 3 in down to a few millimetres a lapping jig can be used to hold the material while it is lapped see image 3 lapping machine and retention jig a jig allows precise control of the orientation of the specimen to the lapping plate and fine adjustment of the load applied to the specimen during the material removal process due to the dimensions of such small samples traditional loads and weights are too heavy as they would destroy delicate materials the jig sits in a cradle on top of the lapping plate and the dial on the front of the jig indicates the amount of material removed from the specimen two piece lapping edit where the mating of the two surfaces is more important than the flatness the two pieces can be lapped together the principle is that the protrusions on one surface will both abrade and be abraded by the protrusions on the other resulting in two surfaces evolving towards some common shape not necessarily flat such as the valves and their seats in an internal combustion engine separated by a distance determined by the average size of the abrasive particles with a surface roughness determined by the variation in the abrasive size this yields closeness of fit results comparable to that of two accurately flat pieces without quite the same degree of testing required for the latter schematic of two piece lapping one complication in two piece lapping is the need to ensure that neither piece flexes or is deformed during the process as the pieces are moved past each other part of each some area near the edge will be unsupported for some fraction of the rubbing movement if one piece flexes due to this lack of support the edges of the opposite piece will tend to dig depressions into it a short distance in from the edge and the edges of the opposite piece are heavily abraded by the same action the lapping procedure assumes roughly equal pressure distribution across the whole surface at all times and will fail in this manner if the workpiece itself deforms under that pressure accuracy and surface roughness edit lapping can be used to obtain a specific surface roughness it is also used to obtain very accurate surfaces usually very flat surfaces surface roughness and surface flatness are two quite different concepts a typical range of surface roughness that can be obtained without resorting to special equipment would fall in the range of 1 to 30 units ra average roughness usually microinches surface accuracy or flatness is usually measured in units of helium light band hlb one hlb measuring about 280 nm 1 1 10 5 in again without resort to special equipment accuracies of 1 to 3 hlb are typical though flatness is the most common goal of lapping the process is also used to obtain other configurations such as a concave or convex surface measurement edit flatness edit the easiest method for measuring flatness is with a height gauge positioned on a surface plate you must set up the part on three stands and find the minimum variation while adjusting them just placing the part on the surface plate and using a dial indicator to find tir on the opposite side of the part measures parallelism flatness is more easily measured with a co ordinate measuring machine but neither of these methods can measure flatness more accurately than about 2 5 μm 9 8 10 5 in optical flats in a wooden case another method that is commonly used with lapped parts is the reflection and interference of monochromatic light 1 a monochromatic light source and an optical flat are all that are needed the optical flat which is a piece of transparent glass that has itself been lapped and polished on one or both sides is placed on the lapped surface the monochromatic light is then shone down through the glass the light will pass through the glass and reflect off the workpiece as the light reflects in the gap between the workpiece and the polished surface of the glass the light will interfere with itself creating light and dark fringes called newton s rings each fringe or band represents a change of one half wavelength in the width of the gap between the glass and the workpiece the light bands display a contour map of the surface of the workpiece and can be readily interpreted for flatness in the past the light source would have been provided by a helium neon lamp or tube using the neon 632 8 nm line citation needed or mercury vapor green line but nowadays a more common source of monochromatic light is the low pressure sodium lamp citation needed today laser diodes and leds are used both being inexpensive and narrow band light sources with semiconductor light sources blue is an option having a smaller wavelength than red for a more thorough description of the physics behind this measurement technique see interference roughness edit surface roughness is defined by the minute variations in height of the surface of a given material or workpiece the individual variances of the peaks and valleys are averaged ra value or quantified by the largest difference from peak to valley rz roughness is usually expressed in microns a surface that exhibits an ra of 8 consists of peaks and valleys that average no more than 8 μm over a given distance roughness may be also measured by comparing the surface of the workpiece to a known sample calibration samples are available usually sold in a set and usually covering the typical range of machining operations from about 125 μm ra to 1 μm ra surface roughness is measured with a profilometer an instrument that measures the minute variations in height of the surface of a workpiece see also edit flat honing a variation of very fine grinding lapping film a lapping consumable stropping which often includes lapping action in its action superfinishing another micro scale subtractive finishing operation surface metrology measuring the effects of such processes references edit english r e 1953 optical flats in ingalls albert g ed amateur telescope making book three scientific american pp 156 162 external links edit mark irvin engis corporation february 2011 diamond lapping and lapping plate control pdf production machining gardner publications archived from the original pdf on 2012 04 25 retrieved 2011 11 17 v t e metalworking v t e machining and computing computer aided engineering 2 5d cad cam g code numerical control nc and cnc stewart platform drilling and threading die head drill drill bit drill bit shank drill bit sizes drilling list of drill and tap sizes tap and die tap wrench threading grinding and lapping abrasive abrasive machining angle grinder bench grinder coated abrasive cylindrical grinder diamond plate flick grinder grinding grinding dresser grinding machine grinding wheel jig grinder lapping sanding sharpening stone spark testing surface grinder tool and cutter grinder machining boring broaching electrical discharge machining electrochemical machining electron beam machining end mill engraving facing hobbing jig borer machine tool machining metal lathe milling milling cutter pantograph photochemical machining planer reamer rotary transfer machine shaper skiving turning ultrasonic machining machine tools angle plate chuck collet fixture indexing head jig lathe center machine taper magnetic switchable device mandrel rotary table wiggler terminology cutting fluid machining vibrations speeds and feeds swarf tolerance tool and die making tramp oil workpiece casting fabrication forming jewellery machining metallurgy smithing tools and terminology welding authority control databases national united states france bnf data israel other yale lux retrieved from https en wikipedia org w index php title lapping oldid 1302038243 category grinding and lapping hidden categories articles with short description short description is different from wikidata articles needing additional references from august 2009 all articles needing additional references all articles with unsourced statements articles with unsourced statements from march 2009 this page was last edited on 23 july 2025 at 01 16 utc page was rendered with parsoid text is available under the creative commons attribution sharealike 4 0 license additional terms may apply by using this site you agree to the terms of use and privacy policy wikipedia is a registered trademark of the wikimedia foundation inc a non profit organization privacy policy about wikipedia disclaimers contact wikipedia legal safety contacts code of conduct developers statistics cookie statement mobile view search search toggle the table of contents lapping 19 languages add topic